The present invention discloses novel improvements to a word processor described and illustrated in copending U.S. patent application Ser. No. 841,830, filed Oct. 13, 1977, which is assigned to the same assignee as this application.
Prior art devices of comparable function comprise automatic typewriters which allow editing of input data subsequent to playback. More specifically, the typist types in the data for printing and backspaces and types over to correct mistakes. Then, a button is depressed and the entire page is automatically printed or typed in corrected form.
Such an automatic typewriter, while allowing efficient correction of mistakes, suffers from several disadvantages. The page, while being initially typed, becomes cluttered and hard to read if there are a number of typeovers. This increases the possibility for error. It is not difficult to overlook a typographical error on a cluttered page and such an error requires correction and a second playback to produce an errorless copy. Another disadvantage of the typical automatic typewriter is slow operating speed. The typewriter may not be used to compose another page until the playback or printing of the first page is completed.
Another prior art device comprises a cathode ray tube which displays an entire page of printed characters. Subsequent to composing and correction of errors on the screen, that is, only after composition and correction of errors of the entire page, the entire page is printed. These systems suffer from the same drawback in that the display is inaccessible during printing.
Yet another drawback of such systems is that the display does not correspond to the printed page under some circumstances. It cases where the backspace and typeover functions, for example, are used to produce a Japanese Yen symbol ( ) by superimposing an equal sign (=) on the capital letter (Y), the position of subsequent data on the display does not correspond to the data as printed. This is because the printer has various control functions which are not provided to the display.